Over the 4 year funding of this grant (RO1 DK92460) we have made major strides in understanding why acute pancreatitis (AP) presents more often as severe AP (SAP) in obese patients. We discovered that the several pounds of excess triglyceride stored in adipocytes within and around the pancreas can get hydrolyzed by pancreatic lipases during AP in a vicious unregulated phenomenon termed fat necrosis, and release large amounts of unsaturated fatty acids (UFAs). Fat necrosis of SAP has prognostic value unlike the pancreatic lipase independent fat stranding noted in diverticulitis, appendiciti etc. UFAs released from fat necrosis in the pancreas worsen pancreatic necrosis and those from fat surrounding the pancreas cause distant organ (e.g. lung and kidney) injury. UFAs damage via increasing cytosolic calcium and inhibiting mitochondrial complexes I and V. These findings have huge implications regarding how FDA recommendations on fat consumption affect the course of AP, and also offer an avenue to therapeutically target the pathophysiology converting AP->SAP. PRELIMINARY DATA: Human: 1) 22 papers from different countries over the last 25 years show studies from countries consuming less milk (richest source of saturated fat) and more fish (high in UFAs) reported SAP at lower body mass index than vice versa. 2) Necrotic collections from the pancreas of SAP patients have very high concentrations of UFAs, as do the sera of SAP patients. 3) Dietary UFAs enrich in the fat stored during obesity. Basic: 1) Changing the fatty acids supplemented to fat cells or mice correspondingly changes the composition of stored triglyceride, with saturated fatty acids (SFAs) causing a milder AP vs. UFAs 2) Pancreatic lipases (i.e. pancreatic triglyceride lipase; PTL and pancreatic lipase related protein 2; PLRP2) and colipase are enriched in fat necrosis 3) PLRP2 alone can damage adipocyte membranes by its phospholipase activity, potentially giving PTL, colipase access to the triglyceride droplet stored in adipocytes. 4) PTL which forms 80-90% of pancreatic lipase may play a major role in hydrolyzing the triglyceride stored in fat. 5) Colipase is essential for ft necrosis mediated by both PTL and PLRP2. 6) This fat necrosis releases large amounts of cytokines (IL-6 and MCP-1) and free fatty acids. PROPOSAL: Aim 1: Study the impact of changing the fatty acids supplemented to adipocytes and mice on the severity of fat necrosis, inflammatory mediator generation, distant cell and organ injury during AP. If SFAs protect, this is a case to present to the FDA. Aim 2: A) Study how adipocyte membrane phospholipid affects their susceptibility to the phospholipase activity of PLRP2 causing their death. B) Study if the PLRP2 remaining in PTL-/- mice can cause SAP and fat necrosis, or if this requires PTL. Identifying and Inhibiting the culprit lipase has therapeutic relevance for SAP Aim 3: Establish the role of colipase in fat necrosis and SAP by omitting colipase, using colipase mutants in vitro and obese conditional colipase knockout mice, and immuno-neutralizing colipase during SAP. If effective, colipase neutralization could be a therapy for SAP.